Strain gage based transducers for translating an input of mechanical energy into equivalent electrical signals are well-known in the art. Force-measuring transducers, referred to as "load cells", typically comprise a "spring element" or "flexure element" of metal with strain gages bonded to its surface to measure bending, direct stress, or shear. For purposes of this application the physical structure incorporating the spring or flexure element will generally be referred to as a "transducer body".
In terms of force-measuring capacity there are generally two classes of transducer body: low capacity bodies of the "bending element" type, for example rings and cantilever beams; and, high capacity bodies of the shear-web and column types.
Cantilever-beam and ring-shaped transducer bodies are relatively flexible, low force transducer bodies, being useful for measuring only up to about 1,000 pounds of force.
In the high capacity category, I-beam and column shapes excel for axial loading above 1,000 pounds, but present unique problems in terms of accurate measurement, for example "cross-talk" errors from off-axis load and bending components. For these and other reasons, column-type load cells have been noted by at least one well-known authority as waning in popularity.
FIG. 1 illustrates a prior art column type transducer body in solid lines, with an alternate I-beam style illustrated in phantom lines. The transducer body of FIG. 1 includes ends designed to be threaded into axial connection with two objects between which a force is generated, for example a hydraulic cylinder and tool operated by the cylinder. Transducer bodies of the type illustrated in FIG. 1 are sometimes referred to as "single-axis envelopes" because they are designed for single-axis load measurements.
As noted above, single-axis column or I-beam type transducer bodies such as those illustrated in FIG. 1 are typically preferred for higher force-measuring applications, i.e. over 1,000 pounds. Below that range the column and I-beam shapes do not deform sufficiently, or have to be made too small in diameter to be usefully stable.